"Between 9,000 and 10,000 accounts or devices were specified in those requests, which came from federal, state and local authorities and included both criminal investigations and national security matters," Apple said in a news release.

Most common are requests from police investigating robberies and other crimes as well as searching for missing children, trying to locate a patient with Alzheimer's disease or hoping to prevent a suicide, Apple said.

"Regardless of the circumstances, our Legal team conducts an evaluation of each request and, only if appropriate, we retrieve and deliver the narrowest possible set of information to the authorities. In fact, from time to time when we see inconsistencies or inaccuracies in a request, we will refuse to fulfill it," Apple said.

Apple disclosed the number of law enforcement data requests two weeks after The Guardian and Washington Post newspapers reported that major Internet companies were indiscriminately sharing customer data with the National Security Agency (NSA) via a program called Prism that gives the NSA "direct access" to those company's servers.

Apple has denied any involvement in the program, saying that it first heard of the Prism program when it was asked about it on June 6. "We do not provide any government agency with direct access to our servers, and any government agency requesting customer content must get a court order," Apple said on Monday.

"We don't collect or maintain a mountain of personal details about our customers in the first place," Apple said, adding that there are certain categories of information which it does not provide to law enforcement or any other group because it doesn't retain it.

Messages sent over iMessage or FaceTime for example are protected by end-to end encryption, Apple said. No one but the sender and receiver can see or read them, Apple added.

"Apple cannot decrypt that data. Similarly, we do not store data related to customers' location, Map searches or Siri requests in any identifiable form," it added.

For this disclosure, Apple asked the U.S. government for permission to report how many requests it has received relating to national security and how they are handled. But Apple was only authorized to share some of that data.

Over the weekend, Facebook and Microsoft also disclosed some data about law enforcement data requests. Microsoft said it had received between 6,000 and 7,000 requests for the six months ending December 31, while Facebook said it had received between 9,000 and 10,000 in the same period.

The amount of transparency that Facebook and Microsoft were allowed to offer about those requests was very limited and similar to Apple's. The law enforcement requests might or might not include requests related to the Foreign Intelligence Surveillance Act (FISA), but companies aren't allowed to say so, according to Microsoft.

Loek is Amsterdam Correspondent and covers online privacy, intellectual property, open-source and online payment issues for the IDG News Service. Follow him on Twitter at @loekessers or email tips and comments to loek_essers@idg.com